Functional relationship between chlorophyll content and leaf reflectance, and light‐capturing efficiency of Japanese forest species

We examined the functional relationship between chlorophyll concentrations and light spectral absorption in 16 species of woody, vine and herbaceous plants in northern Japan. Leaves of each species from under forest shade and in more open sites were measured for chlorophyll, specific leaf area (SLA) and spectral absorption. In all species, SLA increased and the Chl a:b ratio declined in shade‐ vs open‐grown leaves indicating an adaptive adjustment to forest shade in these leaf characters. However, the expected increase in the ratio of 680 to 700 nm absorption in shade leaves did not occur in all species. Light absorption at 680 relative to 700 nm was lower in the shade leaves of Acer japonicum. Kalopanax pictus, Panax japonicus and Petasites japonicus even with a reduced Chl a:b, a commonly accepted indicator of shade adaptation. Therefore, spectral measurements in these species failed to support Chl concentrations that were expected to confer an improvement in the absorption of red light (<680nm) deficient relative to far‐red light (>700 nm) in the forest shade. Compared with other species, the absorption pattern of these four ‘non‐conforming’ species is associated with a higher ratio of shade:open leaves in reflectance spectra in the 600–750 nm range. This suggests an increased reflectance in shade leaves caused by changes in leaf surface properties which are not immediately apparent. We conclude that adaptive spectral absorption cannot always be inferred from changes in specific leaf area and chlorophyll a and b concentrations.